Project Summary Triple negative breast cancer (TNBC) accounts for up to 20% of all breast cancer cases and presents with the worst clinical outcomes due to lack of targeted therapeutic options and rapid onset of tumor recurrence, chemotherapy resistance and metastasis. A phenotypic change within the cancer cells, known as the epithelial to mesenchymal transition (EMT), has been observed to promote cell survival against drug treatment and foster metastatic progression. FOXQ1 has been identified as a potent oncogenic transcription factor that induces the EMT phenotype in TNBC. Preliminary data have uncovered a potential mechanism for the regulation of FOXQ1 transcriptional activity. Protein interaction screening identified binding between FOXQ1 and the MLL core complex, a prominent epigenetic regulatory complex. Further investigation identified that FOXQ1 and the MLL core complex co-localize within the chromatin regions of transcriptional regulatory elements of genes with known functions in inducing EMT. This suggests that the MLL core complex is functioning as a transcriptional coactivator for FOXQ1 to drive the EMT transcription program and resultant tumor progression. Aim 1 will fully interrogate the biochemical nature of this protein interaction by mapping the structure of the FOXQ1-MLL core complex binding pocket. Identification of the critical interacting domains will be accomplished by GST-pull down with recombinant purified proteins. Mapping will be accomplished by successive generation of protein truncations and point mutations, as well as, in silico structural modeling. Aim 2 will elaborate on the functional implication of the FOXQ1-MLL complex interaction. The biochemical insights gained from Aim 1 will but utilized to generate a FOXQ1 construct with induced synthetic mutations that diminish the ability of FOXQ1 to interact and recruit the MLL core complex. The resultant FOXQ1 mutant will be ectopically expressed in a cell line model of breast EMT. The model system will be used to assess the extent to which disrupting FOXQ1 binding to the MLL core complex attenuates the ability to drive features of EMT, cell invasion and distant metastatic progression in vivo. The results of this study will be used to evaluate the efficacy of targeting the FOXQ1-MLL core complex protein interaction as a potential pharmacologic strategy to prevent tumor progression in triple negative breast cancer.